Relative paths for wyBuild theme images

Our project can be built by different developers. We want to change to using our own theme but there doesn't seem to be a way of specifying the Header and Finish images starting from the project directory. Adding the images to "C:\Program Files (x86)\wyBuild" allows you to specify the image without a full path, but obviously that directory is not part of source control. Is there a control word similar to the way you can say "%file%" for the download sites paths that allows setting a relative path for the theme images?